Why old system of measurement isn't accepted nowadays ​

We can measure the length of an object by using 'hand span', 'forearm length', or 'footstep' as the units of measuring length. But hand span, forearm length and footstep cannot be used as a standard unit's measurements because their length is not the same for all the persons.

these muscles maintain the blood pressure in the vessels. the smooth muscles are innervated by nerves of the autonomic nervous system. when the muscles contract, they cause vasoconstriction of the vessels and increase blood pressure. when the muscles relax, they enable vasodilation of the   blood vessels hence reduce blood pressure.